1999
Laminated Coamings
by Philip Jacobs
Stitch and tape kayaks typically use some type of laminated coaming to strengthen the cockpit area and to provide a place for attaching the spray skirt. These coamings consist of a lower portion, which provides the height, and an upper portion, which provides the outer lip to hold the shock cord of the skirt.
While it's possible to make the lower portion out of solid wood spacers, most boats I've seen use concentric rings of plywood, laminated on top of each other, to form both parts of the coaming. By laminating the rings directly on the kayak, the individual layers can flex and conform to the exact shape and contour of the deck.
The simplest coamings are made out of full sized plywood rings of the appropriate number and thickness. Due to the size of the cockpit, and the big hole in the center, however, this uses a lot of wood. Since only the top ring is visible on the finished boat, it's possible to make the lower rings out of segments, using up small scraps left over from the hull, cockpit cut-out, etc.
Being 'thrifty', and determined to make my boat out of just 2 sheets of plywood as the designer promised, I went the segmented route. I used 5 layers of 3mm marine plywood for the lower portion of the coaming (about 19/32nds of an inch, total), and 2 more for the top portion (about _ of an inch). The first 6 rings were each made out of 4 segments, while the top ring was made out of only 2 segments for appearance, yielding a total of 26 segments laminated to form a solid coaming. Quite a number, considering that there were only 6 panel segments used to form the entire rest of the boat!
The keys to simplify laminating all of these pieces are a cutting pattern, and registration pins. I couldn't find a cockpit pattern of the exact size and shape I wanted, so I drew one on a computer using a simple draw program; this let me get smoother curves and more uniform transitions than I could achieve with paper and a compass. The pattern printed out on about 9 letter-sized pieces of paper which were then aligned and taped together, then attached to a piece of poster board with contact cement and cut out. Drawing additional lines or a grid across the cockpit pattern helps in registering the pieces of paper.
The center of this pattern is used to mark the cockpit cut-out on the deck; the pattern itself is used to mark the concentric rings for the coaming. Note that the upper rings are about _ inch wider than the lower rings, to provide a lip for the spray skirt, so either make 2 patterns, or else mark the upper rings first, then cut the pattern down for the lower rings.
I marked the top ring first, to take advantage of the largest pieces of scrap with the nicest looking grain, then cut the others. It is not necessary to use the same number of segments for each layer, as long as they each form a continuous ring when assembled. If each layer will be segmented exactly the same, the pattern can be cut into segment sized pieces to simplify marking. It's a good idea to mark each segment to identify its layer, top, and position, to help avoid problems when the epoxy starts setting up faster than expected and things get hectic.
Stack each ring of the lower portion of the coaming only in place around the cockpit opening without any glue or resin, to get everything lined up and finessed in place. Spring clamps work well for this, and access to large numbers of these really helps. If the segments wiggle a little bit, give more attention to lining them up flush on the inside of the ring (cockpit side). When everything is lined up, drill small holes, slightly larger in diameter than the flat-headed nails to be used for alignment pins, through the stack of coaming segments and the deck below. Drill enough holes so that there is at least one alignment hole through each segment. Remove the segments and stack them in a way that makes sense to you.
Tape a few pieces of waxed paper from the kitchen across the deck near the cockpit opening, and cut away the paper so that it hangs an inch or so over the opening. Place some additional waxed paper or plastic inside the hull to catch any epoxy drips. Insert the registration nails up from underneath the deck, and use small strips of masking tape to hold them in place and to prevent any epoxy leaks. Mix up some epoxy and coat the tops and connecting edges only of the segments which form the first layer and place them over the registration nails. Coat the tops, bottoms and connecting edges of the successive segments, and stack them in place, holding them with spring clamps.
By mixing small batches of epoxy, the individual rings can be laminated one or two at a time, if desired, allowing for a few hours between each layer. Don't coat the top surfaces with epoxy until laminating the next layer, and remove the registration nails after the epoxy starts to set up, unless you want them to become a permanent part of the boat. Re-drill the holes before laminating the next layer.
After the complete lower portion of the coaming has cured, remove it from the boat as a single unit. The formed coaming must be handled carefully, but still can be gently clamped to smooth and blend the outside edge using a block plane or spoke shave. A stationary belt sander also works well. Sealing this edge with epoxy, and even pre-sanding it for varnishing, is much easier to do at this stage than after it is sandwiched between the deck and upper coaming.
Clamp and glue the lower coaming section to the deck using the same registration nails, and use the same procedure for the upper portions of the coaming, except for the nails which shouldn't be used for the top layer. I had good success blending the inside of the coaming and cockpit smooth using a sharp spokeshave and a sanding drum on a Dremel tool, followed by light hand sanding.
